Across San Juan Bay from Cataño is the little islet that started it all-- Viejo San Juan.  Almost half a millennia in the making (the city was founded in 1521) Old San Juan is narrow streets, blue cobblestones and cerulean seas crashing on the impregnable castles that guarded this lifeline of the Spanish Empire for centuries.  We like taking folks along the Paseo Princesa to the Fuente de Raices then on to the city gate.  From there you can pass the gates to the Fortaleza (the governor's mansion and oldest executive mansion still in use in the United States) before climbing the hill up to the cathedral (San Juan Bautista) where Floridians can pay respects to their founder (Juan Ponce de Leon) who is entombed on the left side of the cathedral.  We suggest touring Castillo San Cristobal instead of El Moro.  It's smaller and less exhausting, but no trip to San Juan should be made without a tour of one of the castles.